The present invention relates to a valve mechanism for an automotive engine, and more particularly to a valve mechanism provided with a shaft-mounted rocker arm of a divided type.
Such a valve mechanism is disclosed in Japanese Utility Model Application Laid Open Nos. 57-193905, 58-22402, and 58-98407, in which a valve mechanism is provided with a rocker arm divided into an actuating arm member for operating a valve and a rocker arm member to be rocked by a cam. The rocker arm member is adapted to be engaged with the actuating arm member for operating the valve.
As shown in FIGS. 11 to 14, a conventional valve mechanism comprises a rocker-arm shaft 31, a sleeve 32 slidably mounted on the shaft 31. The sleeve 32 has a plurality of splines 32a and projections 32b formed between splines 32a. A groove 32c is formed on the projections 32b. An actuating arm 33 mounted on the shaft 31 has a plurality of splines 33a corresponding to the projections 32b of the sleeve 32 to be detachably engaged therewith. A rocker arm member 34 provided to be engaged with a cam 40 mounted on a camshaft is mounted on the sleeve 32. The rocker arm member 34 has a plurality of splines 34a each of which is engaged with the projection 32b. A ramp 35 is formed on the rocker arm member 34. A stopper 36 operated by the ramp 35 is engaged with groove 32c of the sleeve 32. The sleeve 32 is axially shifted on the shaft 31 to the right by oil pressure and returned by a spring (not shown). When the rocker arm member 34 is rocked by the cam 40, at the same time, the stopper 36 is lifted by the ramp 35 so as to be disengaged from the groove 32c.
In operation, as shown in FIG. 12, the stopper 36 is engaged with the groove 32c. Although the oil pressure urges the sleeve 32 to shift in the right direction, sleeve 32 maintains the position. When the rocker arm member 34 is rocked and the ramp 35 pushes up the stopper 36, the stopper is disengaged from the groove 32c. Thus the sleeve 32 is shifted by oil pressure as shown in FIG. 13. However, in this state, the splines 34a of rocker member 34 are not corresponding to the splines 33a of actuating arm 33. Accordingly, splines 32a of the sleeve 32 can not be engaged with the arm 33. As the cam 40 rotates to engage with the rocker arm member 34 at a base circle 40a of the cam 40, the rocker arm member 34 is rocked so as to correspond the splines 34a to the splines 33a. Thus, as shown in FIG. 14, the projections 32b are inserted into the splines 33a to integrate the rocker arm 34 with the arm 33, thereby forming a single rocker arm. Accordingly, the valve stem 41 is operated.
In such a mechanism, the engaging operation of the rocker arm member and actuating arm is performed in a synchronized state. However, when the oil is drained, the sleeve is immediately shifted to release the projections from the splines of the actuating arm member 33 by the spring at any time, which will cause the breakdown of splines and projections.